1. Field of the Invention
The present invention is concerned with a process for treating water containing volatile compounds and toxic compounds and with the ultimate disposal or destruction of these compounds.
2. Information Disclosure Statement
Aerobic biological treatment of wastewaters which contain volatile compounds can result in the emission of the volatile compounds into the environment. The volatile compounds are stripped from the aqueous phase during the process of transferring oxygen to the wastewater. Whether the aeration is accomplished by bubble or surface aeration makes little difference in the volatilization affect.
Studies by Weber and Jones, "Toxic Substance Removal in Activated Sludge and PAC Treatment Systems", EPA/600/S2-86/045, June, 1986 demonstrated that addition of powdered activated carbon to an aerobic biological system results in greatly reduced stripping of volatile compounds.
The addition of powdered adsorbent to the activated sludge process aeration basin constitutes the Powdered Activated Carbon Treatment (PACT.TM.) process, examples of such process are described in U.S. Pat. Nos. 3,904,518 and 4,069,148. The preferred powdered adsorbent is powdered activated carbon and it is generally economical to regenerate the powdered carbon once its adsorptive properties are expended and to reuse the regenerated carbon in the treatment process. An efficient method of carbon regeneration is wet air oxidation of the mixture of biological solids and spent carbon. Wet air oxidation at temperatures of 400.degree. to 550.degree. F. (204.degree. to 288.degree. C.) and pressures of 350 psig to 1900 psig (2413 to 13,100 KPa) destroys the volatile portion of the biological solids and oxidizes the organic substances adsorbed on the surface of the powdered carbon restoring adsorptive capacity. The resulting regenerated carbon is recycled to the treatment process.
An alternative method of carbon regeneration and biological solids disposal is controlled flame incineration operating under limited oxygen conditions. This thermal regeneration is generally carried out under a controlled atmosphere such as in a multiple hearth furnace. The hot thermally regenerated carbon and biomass residue mixture is cooled by introduction into a water quench tank. The resulting aqueous slurry of regenerated carbon is recycled to the treatment process.
Some contaminated wastewaters may contain such high concentrations of volatile compounds that even the PACT.TM. treatment system cannot retain all of the volatile compounds in the aqueous phase during aeration.
Air stripping often is used to intentionally remove volatile compounds from water or wastewater. This process is well known in the art and generally involves counter-current contact of water and air in a stripping tower with contaminated water passing down the tower over a packing and air directed up from the bottom to strip out the volatile compounds. A mechanical blower is often employed to introduce air into the bottom of the tower.
This air stripping only results in transfer of the volatile compounds from the aqueous phase to the gaseous phase and does not address final disposal of these volatile compounds. The problem is particularly serious where high concentrations of volatile compounds are present in the water.
In related publications, Copa, et al in U.S. Pat. No. 3,828,525 disclose removing contaminants and objectional odors from wet air oxidation gases by scrubbing with activated sludge or a mixture of activated sludge and fresh sewage.
Burant, et al in Canadian Pat. No. 1,104,795 disclose removing objectionable contaminants from odorous gas streams by scrubbing with an aqueous suspension containing both biological solids and activated carbon.
The present invention provides an effective and useful method of treating water contaminated with volatile compounds or toxic compounds, as well as the ultimate disposal of these substances.